1. Technical Field
The disclosure relates to discharge lamp driving devices, and particularly to a protection circuit of a discharge lamp driving device.
2. Description of Related Art
With the development of lighting technology, in many lighting devices, such as liquid crystal display (LCD) devices, at least two groups of discharge lamps are commonly employed for achieving a better lighting effect to meet practical lighting requirements. Typically, in order to protect the lighting device from being damaged under the circumstance that one or more of the at least two groups of discharge lamps are short or open, an open protection circuit and a short protection circuit are configured in the lighting circuit. The open and short protection circuits provide protection signals to control current input to the discharge lamps, thereby protect the lighting device from being damaged or destroyed by very high voltage.
Referring to FIG. 3, a schematic diagram of a conventional discharge lamp driving device 10 is shown. The discharge lamp driving device 10 includes a power stage circuit 100, a control circuit 101, a feedback circuit 102, a lamp protection circuit 103, and a transformer circuit 104. The lamp protection circuit 103 includes a current sensing circuit 1031, an open protection circuit 1032, and a short protection circuit 1033. When a first lamp L1 or a second lamp L2 is open, current signals flowing through the first lamp L1 and the second lamp L2 are sensed respectively by a first current sensing unit 1031A and a second current sensing unit 1031B, and are transmitted to the open protection circuit 1032. Subsequently, the open protection circuit 1032 transforms the current signals to an open circuit protection signal, and transmits the open circuit protection signal to a control circuit 101. The control circuit 101 transforms the open circuit protection signal to a control signal to control the output of the power stage circuit 100 to the first lamp L1 and the second lamp L2. Thereby, the lamps L1 and L2 are protected.
Similarly, when the first lamp L1 or the second lamp L2 is shorted, the current signals flowing through the first lamp L1 and the second lamp L2 are sensed respectively by the first current sensing unit 1031A and the second current sensing unit 1031B, and are transmitted to the short protection circuit 1033. Subsequently, the short protection circuit 1033 transforms the current signals to a short circuit protection signal, and transmits the short circuit protection signal to the control circuit 101. The control circuit 101 transforms the short circuit protection signal to a control signal to control the output of the power stage circuit 100 to the first lamp L1 and the second lamp L2. Thereby, the lamps L1 and L2 are protected.
In the discharge lamp driving device 10, the open protection circuit 1032 and the short protection circuit 1033 are independent of each other. Accordingly, two sets of voltage dividing resistors and crystal field-effect transistors (FETs) are generally needed. In addition, the open protection circuit 1032 or the short protection circuit 1033 may wrongly output a protection signal when either of the lamps L1 and L2 is operating normally albeit at a higher voltage than usual. That is, the protection function of the discharge lamp driving device 10 may be unreliable.